1. Field of the Invention
The present invention relates to a lane recognition device which recognizes a relative position of a vehicle and a lane mark, by detecting the lane mark partitioning a traffic lane of a road.
2. Description of the Related Art
Conventionally, there is proposed a technique of calculating a relative distance and the like of the lane mark and the vehicle, by obtaining a road image in each predetermined control cycle by a camera mounted on a vehicle, collecting candidates of image portion of the lane mark detected from each road image from a predetermined short period of time, and converting a camera coordinate of each image portion to a real space coordinate (for example, refer to Japanese Patent No. 3538476).
In the conventional technique mentioned above, the real space position of the lane mark is recognized by collecting the candidates of the image portion of the lane mark detected from the road images obtained in each continuing control cycle from a predetermined short period of time, and converting the same to the real space coordinate. In this case, as a criterion of a reliability of the recognition of the real space position of the lane mark, an average detection rate of lane mark in a predetermined period immediately before is generally used, as is shown in FIG. 8.
In FIG. 8, the results of the lane mark detection processing executed in each control cycle T10 are indicated by o when the lane mark is detected, and by x when the lane mark is not detected. Further, the time when it is judged that the reliability of the lane mark detection is high and the recognition of the relative position of the lane mark and the vehicle is executed is indicated by o, and the time when it is judged that the reliability of the lane mark detection is low and the recognition of the relative position of the lane mark and the vehicle is stopped is indicated by x.
As for the reliability of the lane mark detection, when the number of the cycles in which lane mark is detected is equal to or more than m in a period of n cycles (t11-tp1) immediately before the time of judgment tp1, it is judged that the reliability of lane mark detection is high, and the relative position of the lane mark and the vehicle is recognized.
In this case, when it is switched from the state where the lane mark is not detected (the state where x continued, until t14) to the state where the lane mark is detected (transit from x to o, t15 onward), the reliability of lane mark detection is not judged to be high until lapse of time corresponding to at least m times T10, so that the recognition of the relative position of the lane mark and the vehicle cannot be started.
Therefore, when the vehicle temporarily travels on a section in which the lane mark is not laid, for example in the case where the vehicle passes through an intersection, or in the case where the vehicle travels in a branching or a converging point at an interchange, the recognition of the relative position of the lane mark and the vehicle stops from the decrease in the reliability of lane mark detection. Thereafter, a certain period of time is necessary until it is judged that the reliability of lane mark detection is high even after it is returned to the state where lane marks are laid.
In this case, even when the vehicle passes through the intersection or the branching or the converging section and returns to the state where it is possible to steadily detect the lane mark, the state where the recognition of the relative position of the lane mark and the vehicle is stopped continues. Therefore, there is an inconvenience that it is not possible to promptly resume a lane maintaining control of assist driving a steering in order to maintain the traffic lane, or a departure warning control from the traffic lane and the like.